> > snipped-for-privacy@aol.com wrote in sci.electronics.design and
> >rec.crafts.metalworking:
> >> I have ordered an LCR meter and a less expensive cap sub box that
> >> should be rated 200 VDC instead of 50 VDC.
> >> Doug
> >The LCR meter has arrived from Hong Kong.
> >The inductance of the motor coils in parallel is 112 microhenries.
> >The resonant capacitance is (confirm?) 62 microfarads.
> >There are 36 poles on this split-capacitor motor.
> >The synchronous speed would be (confirm?) 400 rpm.
> >The motor runs at 225 (rated) rpm.
> >The motor runs with 175/400 = 44% slip.
> >I need to run the motor at 400+44% = 576 rpm.
> >I have to do that because of the impedance protection, right?
> >So the efficiency will indeed be low.
> >At 90 pedal rpm, with my existing cog, I will need a
> >x * 90 / 8 = 576;
> >x = 576 * 8 / 90 = 51 tooth cog, which is just what I have.
> >However, if I splice two motors together at 225 rpm, I will have to > >recompute.
> >I recall that damping reduces the apparent frequency of an impulse
> >driven resonant system, and wonder if the substantial resistance of
> >this impedance protected motor will reduce the continuously driven
> >resonant frequency, or whether my recollection only applies to impulse
> >driven resonant systems.
> >Yours,
> >Doug Goncz
> I've picked up this thread late so I've probably missed important
> bits. However the following comments may be useful.
> If I've understood the post correctly you are aiming to use an
> impedance protected 36 pole motor as a self excited induction
> generator.
> Self excited induction generators rely on the tiny residual
> pattern of magnetisation of the rotor being reinforced by the current
> flowing in the near resonant stator winding circuit. It has to be
> operating close to resonance for the current build up to be large
> enough to reinforce the rotor field pattern. It has to be on the
> capacitative side of resonance to permit the phase angle of the stator
> current to reinforce the rotor field pattern.
> It is a positive feedback regenerative system and on a large
> efficient motor the output can build up to far beyond its rated motor
> power until limited by magnetic saturation. This effect is sometimes
> used for regenerative braking of single and three phase motors and can
> result in a spectacularly short stopping time.
> With a care and control of speed, self excited induction
> generator systems are possible but they're pretty touchy devices.
> If you're unlucky with the the rotor iron they may not retain enough
> initial magnetism to enable the output to build up (manufacturers
> strive to reduce this because it degrades the efficiency when used as
> a motor) Also it must use a reasonably efficient motor for the
> magnetic feedback to exceed the system losses.
> Efficiency is your major problem. An impedance protected motor
> means a motor with deliberately large leakage inductance so that the
> impedance of this inductance limits the current that flows when the
> motor is stalled or overloaded. With limited stalled current the
> starting torque (already poor because it is a capacitor run machine)
> has to be boosted by the use of a high resistance rotor and this
> results in your observed very high slip speed. Even if there were no
> other losses of any kind the motor efficiency could not be any better
> than the % synchronous speed - 56%. With other losses taken into
> account the motor efficiency is probably no better than 40%.
> With the uH to mH correction your sums are OK but this level
> of efficiency is too low for a succesful induction generator.
> Jim
Many thanks to Jim and other contributors to the thread "Motor/Generator Analysis".
I have put a lot of money and time into this, and I want to give it my best shot, but I don't want to whip a dead horse, so to say.
Frankly, I don't understand magnetics. At least not as I understand resonance. I'm an amateur musician; I understand resonance and know a little about phase shifts near the peak. I do understand that because the slope of the curve is negative on the high-frequency (capacitative)
side of resonance, loading of the generator, within limits, will result
in additional power to meet the load.
But B x I makes my head spin. I'm fine in 3 dimensions. So I get some of it. And I get that in the cylindrical coordinate system, B and I can
be locally orthogonal, and can vary in time, with phase shifts, while being wrapped into a connected topology. I just don't feel that the way
I feel resonances. It's not intuitive.
Would replacing the rotor "windings" with copper wire or bus bar (easy), and rewinding the stator with bigger wire (hard) have any chance at all of working together by lowering the leakage inductance and rotor resistance to allow resonance?
That's my best question; is there any hope at all?
This is a one-off demo, not a production prototype!
Yours,
Doug Goncz Replikon Research Falls Church, VA 22044-0394